The present invention relates to a thermal printer containing a thermal print head. More particularly, the invention relates to heat-transfer thermal printer in which articles and a thermal ink ribbon are caused to simultaneously traverse the thermal print head which selectively heats the ink ribbon to transfer ink to the article in a predetermined pattern. The articles may be any sheet-like material such as paper, film, etc. while the pattern may be a bar code, postal indicia, series of alphanumeric characters or other desired image.
In situations where printing occurs along the entire article, printer throughput is limited by the speed at which the thermal print head operates. However, if printing occurs only on a portion of the article, then printer throughput is also influenced by the speed at which the article can be feed through the printer when there is no printing taking place. Postage meters are an example where printing occurs only on a portion of the article. Typically, a postal indicia occupies only a small portion of the surface of an envelope. Other printing applications, such as: lottery tickets, point of sale consumer receipts, merchandise identification tags or labels, etc., may be similarly situated.
It is well know in the mailing industry to print a postal indicia on an envelope using a postage meter. Postage meters may utilize a variety of technologies to perform the printing process. Traditional postage meters use a rotary die that includes an embossed postal indicia. After applying ink to the die, the die is rotated to engage an envelope and transfer the postal indicia to the envelope. Other postage meters use thermal printing technology to create the postal indicia image on the envelope. In thermal postage meters, the envelope is compressed against a thermal print head by a print or platen roller with a thermal ink ribbon captured there between. To print the postal indicia, the envelope and ink ribbon are simultaneously advanced past the thermal print head while the individual thermal print head elements are selectively heated causing the ink to liquify and transfer to the envelope. Once printing is completed, it is necessary to feed the envelope from the postage meter.
Of particular interest is the thermal postage meter described in detail in U.S. Pat. No. 5,339,280 (C-907), assigned to the assignee of the present invention and incorporated herein by reference. The thermal postage meter described above differs from other thermal printers primarily in that it provides both a print roller and an eject roller for independent control of the envelope which allows for increased throughput without wasting thermal ink ribbon. However, it has been empirically determined that the above referenced thermal postage exhibited numerous problems, some of which are high motor torque requirements and high manufacturing cost.
It is important that the print roller supply adequate force to ensure proper ink transfer from the ribbon to the envelope, but not excessive force which could damage the thermal print head.
It is also important not to smudge the indicia printed on the envelope when feeding the envelope from the postage meter.